The present invention relates generally to the field of acoustics, and in particular to transducers, to communication and power transmission using arrays of transducers, and to optimizing transducer performance when alignment is imperfect or when transducers may move over time.
A transducer is a device that converts a signal in one form of energy to another form of energy. This can include electrical energy, mechanical energy, electromagnetic and light energy, chemical energy, acoustic energy, and thermal energy, among others. While the term “transducer” often refers to a sensor or a detector, any device which converts energy can be considered a transducer.
Transducers are often used in measuring instruments. A sensor is used to detect a parameter in one form and report it in another form of energy, typically as an electrical signal. For example, a pressure sensor might detect pressure—a mechanical form of energy—and convert it to electricity for display for transmission, recording, and/or at a remote location. A vibration powered generator is a type of transducer that converts kinetic energy derived from ambient vibration to electrical energy. Transducers can be particularly useful for transferring power and/or energy through surfaces when it is desirable not to create physical openings in the surface, such as for taking readings inside a pressurized chamber, or through the hull or a water craft.
A transducer can also be an actuator which accepts energy and produces movement, such as vibrational energy or acoustic energy. The energy supplied to an actuator might be electrical or mechanical, such as pneumatic or hydraulic energy. An electric motor and a loudspeaker are both actuators, converting electrical energy into motion for different purposes.
Some transducers have multiple functions, both detecting and creating action. For example, a typical ultrasonic transducer switches back and forth many times a second between acting as an actuator to produce ultrasonic waves, and acting as a sensor to detect ultrasonic waves and converting them into electrical signals. Analogously, rotating a DC electric motor's rotor will produce electricity, and voice-coil speakers can also function as microphones.
Piezoelectric materials can be used as transducers to harvest even low levels of mechanical energy and convert them into electrical energy. This energy can be suitable for powering wireless sensors, low power microprocessors, or charging batteries. A piezoelectric sensor or transducer is a device that uses a piezoelectric effect to measure pressure, acceleration, strain, or force by converting those physical energies into an electrical charge. The piezoelectric effect is a reversible process in that materials exhibiting the direct piezoelectric effect—generation of an electrical charge as a result of an applied mechanical force—also exhibit the reverse piezoelectric effect—generating a mechanical movement when exposed to an electrical charge or field. Thus, piezoelectric transducers can also work in reverse, turning electrical energy into physical vibrational energy and vice versa. Piezoelectric transducers have the dual advantages of working using low energy levels, and at a small physical size. Ultrasonic transducers may be piezoelectric transducers, applying ultrasound waves into a body, and also receiving a returned wave from the body and converting it into an electrical signal.
Construction of piezoelectric-based acoustic-electric channels as a means to transmit both power and data across obstructions, such as pressure vessel walls, has been of significant interest as a way to maintain structural integrity by minimizing the number of mechanical penetrations. It has been shown that these types of penetration replacement systems are capable of fulfilling the required connection characteristics of high power delivery and high data rates, while maintaining the structural integrity of the wall by avoiding the need for significant wall modifications, particularly openings. A typical simple “channel” is composed of a transmitting piezoelectric transducer (transmit transducer) coupled to one side of a wall and a receiving transducer (receive transducer) coupled to the opposite wall surface. An example of such a channel is illustrated in FIG. 1, where the transmit and receive transducers are circular “disk” transducers whose axes are coaxially aligned. Ideally, the transmit and receive transducer or transducers are perfectly aligned across the wall though, as will be explained below, this is not always the case.
These types of channels have been shown to be capable of high data-rate and/or high-power, high-efficiency operation. Work done at Rensselaer Polytechnic Institute has demonstrated that a single data channel constructed using 4 MHZ resonance transducers operating through a 63.5 mm (2.5 in.) thick steel wall is capable of over 12 Mbps throughput using complex communication techniques. See Lawry, T. J., 2011, “A High Performance System for Wireless Transmission of Power and Data Through Solid Metal Enclosures,” Ph. D. Thesis, Rensselaer Polytechnic Institute, Troy, N.Y., and Lawry, T. J., Saulnier, G. J., Ashdown, J. D., Wilt, K. R., Scarton, H. A., Pascarelle, S., and Pinezich, J. D., 2011, “Penetration-Free System for Transmission of Data and Power Through Solid Metal Barriers,” In Military Communications Conf. (MILCOM), 2011, pp. 389-395.
In using multiple, parallel, simultaneously operating channels assembled onto a wall at very close proximity and applying multiple-input-multiple-output (MIMO) techniques to mitigate crosstalk among the channels, it has been shown that the aggregate data-rate throughput approximately increases proportionally with the number of parallel channels. See Ashdown, J. D., 2012, “High-Rate Ultrasonic Data Communication Through Metallic Barriers Using MIMO-OFDM Techniques,” Ph. D. Thesis, Rensselaer Polytechnic Institute, Troy, N.Y.; and Ashdown, J. D., Saulnier, G. J., Wilt, K. R., and Scarton, H. A., “High-Rate Ultrasonic Communication Through Metallic Barriers Using MIMO-OFDM Techniques,” Military Communications Conference (MILCOM), 2012.
Regarding power transmission, relatively high-efficiency and high-power operation has been demonstrated through thick metal walls. See Wilt, K. R., Scarton, H. A., Saulnier, G. J., Lawry, T. J., and Ashdown, J. D., 2012, “High-Power Operation of Acoustic-Electric Power Feedthroughs Through Thick Metallic Barriers,” In Proc. ASME 2012 International Mechanical Engineering Congress and Exposition, and Wilt, K. R., 2012, “Experimentation and Modeling of Piezoelectric-Based Ultrasonic Acoustic-Electric Channels,” Ph. D. Thesis, Rensselaer Polytechnic Institute, Troy, N.Y. That work included demonstrating use of channels composed of 1 MHZ resonance transducers (1 in. diameter) across 57.2 mm (2.25 in.) thick metal test blocks. The channels were optimized and operated at high-power levels. The laboratory tests demonstrated the use of channels capable of upwards of 70% power transfer efficiency, while successfully delivering over 100 W (approximately 140 W maximum) to a dummy load resistor load. Other testing has demonstrated over 1 kW of delivered power through a thin metal wall using specialized transducer geometries. See Bao, X., Biederman, W., Sherrit, S., Badescu, M., Bar-Cohen, Y., Jones, C., Aldrich, J., and Chang, Z., 2008, “High-Power Piezoelectric Acoustic-Electric Power Feedthru for Metal Walls,” In Proc. SPIE Conf. Industrial and Commercial Applications of Smart Structures Technologies, Vol. 6930, p. 69300Z.
One significant issue with transducer channel arrangement, including the above systems, is that the alignment of the transducers has a significant impact on the capabilities of the channel(s). For power delivery, even a small amount of misalignment results in a significant reduction in power transfer efficiency. For communications, a small amount of misalignment is somewhat less of an issue since the operational power levels are low, and because low communication signal transfer efficiency can generally be compensated for by using increased transmit power. Nevertheless, transducer misalignment can make the channel response more complex and can result in a reduced data communication rate. In multi-channel communications arrangements using multiple-input and multiple-output (“MIMO”) techniques, the sensitivity to misalignment errors is not significantly increased, and may actually be reduced, relative to single channel arrangements. This is because MIMO arrangements can be used with techniques to utilize the crosstalk introduced between channels through the misalignment.
Transducer alignment is not a major concern in laboratory environments and some factory environments because precise placement of transducers is relatively trivial. Transducer installation and alignment can be much more difficult, however, when installations are done “in the field” or on previously fabricated structures. In many “real world” implementations, transducer alignment can involve significant dimensional error due to scale, surface inaccessibility, surface irregularity, inability to see both sides of a barrier simultaneously, and other factors. Additionally, in arrangements where the transmit and receive transducers do not share a common rigid mating medium, such as with transducers mounted on two plates that are not rigidly connected together and/or that have a liquid layer between them, transducer alignment may be variable.
FIGS. 2a, 2b and 2c illustrate three generalized alignment cases for a single pair of transducers. Note that the diagrams show some spreading of the acoustic energy beam as the distance from the transmit transducer (on the left) increases. In case (a), the transducers are perfectly aligned and the receive transducer (on the right) captures the maximum amount of the transmitted energy. Case (b) describes a partially aligned channel, where the receive transducer captures a fraction of the transmitted energy. This situation would result in a significant loss in power transfer efficiency and/or potential communications performance loss, such as higher error rates or reduced data transfer rates. The third case, case©, shows the receive transducer completely misaligned with the transmit transducer, resulting in a severely degraded channel.
Methods for aligning transducers across a rigid medium have been described where a non-destructive “pitch-catch” testing techniques are used to “peak” the channels. See Wilt, K. R, 2012, “Experimentation and Modeling of Piezoelectric-Based Ultrasonic Acoustic-Electric Channels,” Ph. D. Thesis, Rensselaer Polytechnic Institute, Troy, N.Y., and Wilt, K. R., Scarton, N. A., Lawry, T. J., Saulnier, G. J., and Ashdown, J. D., 2012 “Method and Apparatus for an Acoustic-Electric Channel Mounting,” U.S. patent application Ser. No. 13/559,164. Filed July 2012. The transducers are aligned by comparing a pressure amplitude signal, created by a stationary “pitching” transducer, at various locations on the opposite side of the barrier as measured by a “catching” transducer. The position on the opposite wall where the strongest signal is detected by the catching transducer is presumed to be directly opposite the pitching transducer sending the signal. Employing multiple pitch-catch channels (e.g., multiple pitching locations) can provide reasonably accurate alignment of the required transmit and receive transducers in some well-suited applications.
Nevertheless, given the losses associated with misalignment and the difficulty in achieving and/or maintaining alignment in some applications, methods and apparatus for optimizing operation despite transducer mis-alignment and alignment variability are needed. New and improved methods to operate misaligned and variably aligned acoustic-electric channels with minimal or even no performance loss will have a variety of applications.
The following references provide background for the instant invention, and are also incorporated to the extent that they might help enable various embodiments of the invention.
U.S. Pat. No. 5,869,767 teaches an ultrasonic transducer including a flexible transmitter, a flexible receiver array, and flexible electrodes for the transmitter and receiver. The elements of the transducer are arranged such that the transducer may be flexed for conformity with surfaces of test specimens of a variety of non-planar configurations.
U.S. Pat. No. 6,546,803 is an ultrasonic probe having a segmented ultrasonic transducer made up of a plurality of individual independent transducers, and a plurality of electrical connections linking each the piezoelectric transducer with a power source.
In U.S. Pat. No. 5,460,046, a method and an apparatus are provided for measuring the wall thickness of a pipeline through which a fluid flows. Each transducer is activated by periodic electrical pulses to cause transmission of acoustic signals in the pipeline fluid that are reflected by the pipeline interior and exterior walls. A plurality of multiple ultrasonic reflections from the pipe interior and exterior walls for each ultrasonic pulse produced by each transducer are analyzed employing a software algorithm embedded in the electronics within the pig body to provide a measurement of pipe wall thickness. By means of an odometer attached to the pig body, electrical signals are provided that reveal anomalies in the wall thickness of the pipeline relative to the distance traveled by the pig body so that an operator can thereby determine the location in the pipeline of wall thickness anomalies.
U.S. Pat. No. 5,311,095 describes an ultrasonic transducer array comprising a ceramic connector having an array of connector pads, a mismatching layer of electrically conducting material connected to the upper surface of the ceramic connector, a piezoelectric transducer chip connected to the mismatching layer, and separation means for dividing the piezoelectric chip into a plurality of transducer elements positioned in a two-dimensional array. Each one of the plurality of transducer elements is selectively connected to a corresponding one of the connector pads. Also disclosed are a two-dimensional ultrasound transducer array and a transducer array for ultrasound imaging.
U.S. Pat. No. 4,514,247 teaches a method for fabricating composite transducers by bonding together plates of active and passive materials to form a laminated block. The active material is preferably a piezoelectric ceramic. Thereafter, a series of cuts are made in the laminated block to obtain a composite plate wherein regions of active material are separated from one another by regions of passive material. The method provides composite transducers having fine structures which can be produced without the difficulty of assembling many small rods or sawing deep, narrow' grooves, as required by other methods.
U.S. Pat. No. 4,546,459 describes, among other aspects, a phased array transducer having a hollow cylindrical or tubular body and having a plurality of acoustic coupling ports and a single electro-acoustical transducer element operating in combination with the ports for providing a broadside vertical directivity pattern. In accordance with one embodiment of the invention for operation in an underwater environment, there is provided a hollow elongated cylindrical tube having closed ends and a plurality of pairs of substantially annular apertures or ports through the wall of the tube and spaced along the longitudinal dimension of the tube.
U.S. Pat. No. 4,211,948 describes an ultrasonic transducer array with high sensitivity for use in water tanks and with human subjects in steered beam imagers to make wide angle sector scans. The array has narrow transducer elements. Steered beam imagers are also known as phased array sector scanners, and the present front surface matched array makes possible wide angle sector scans with a total scan angle exceeding about 60 degrees.
U.S. Pat. No. 6,587,540 is an apparatus and method for imaging objects with wave fields. One embodiment includes two arrays facing each other, with their faces mutually parallel.
UK Patent GB2366603 describes a marine vessel having a plurality of tiles on its surface. Each tile has, integral therewith, an integrated circuit which is programmed to cause piezoelectric elements at the surface of the tile to modify the dynamic properties of the surface of the vessel. This enables turbulence to be reduced, acoustic reflections to be cancelled, escape of noise from the vessel to be eliminated, and acoustic signals to be transmitted as and when necessary. Selected elements act as sensors and others as drivers. The elements may be used on submarines or aircraft.
A 2007 thesis by one Isil Ceren Elmasli, submitted to Bilkent University, is said to describe a study of a two ceramic layer stacked transducer structure for short range underwater communications at high frequencies. The transducer structure has two electrical and two acoustic ports. Ceramic layers are matched to water load through quarter wavelength thick matching layers on each radiating face. It is shown that wide bandwidth operation can be maintained. The beam width of the structure is narrow due to end-fire effect of two back-to-back radiating elements. The document can be retrieved at: http://www.thesis.bilkent.edu.tr/0003273.pdf.